The present invention relates to a brake apparatus effectively using a piezoceramic actuator for producing a braking force.
Brake apparatuses for controlling a vehicle speed or stopping a vehicle are generally classified into drum and disc brakes. The disc brake produces a braking force by bringing friction pads into tight contact with a disc so as to clamp the disc. With a disc brake, a stable and uniform distribution of the braking force can be obtained. In addition, the disc brake has a high heat resistance, an automatic braking force adjustment mechanism can be easily mounted on the disc brake apparatus, and braking noise is minimal. The drum brake apparatus does not have these advantages. For this reason, the disc brake apparatus has prevailed.
In conventional brake apparatuses, a hydraulic cylinder system as a power transmitting means is adapted as an input actuator mechanism to transmit a hydraulic/pneumatic pressure. The friction pads are brought into tight contact with or are separated from the disc in accordance with the depression/release of a brake pedal. In the hydraulic actuator mechanism, a braking force obtained only upon depression of the brake pedal is limited, so a force amplifying device consisting of a master cylinder, a servo unit and so on is adapted to increase the clamping force of the friction pads with respect to the disc.
However, any conventional brake apparatus using the hydraulic actuator mechanism described above requires a master cylinder, a booster, a wheel cylinder and brake fluid piping, resulting in a complicated construction and cumbersome molding and assembly. This leads to not only high cost but also requires extra mounting space. As a safety measure, a plurality of independent brake systems are often arranged in parallel with each other. In this case, the above drawbacks become decisive.
Demand has recently arisen for brake control including a variety of applications such as an anti-skid mechanism. The conventional hydraulic brake apparatuses cannot satisfy this demand.
In order to overcome the conventional drawbacks, an actuator mechanism in the brake apparatus comprises an electric motor or a slurry clutch, as described in Japanese Patent Disclosure No. 56-31532. An electromagnetic brake is used in an actuator mechanism, as described in International Application No. PCT/DE82/00172 (International Disclosure No. W083/01044). Unlike other conventional actuator mechanisms which are mechanically operated, these actuator mechanisms are electrically operated, so that a proper braking force can be quickly produced in a flexible manner.
According to the conventional brake apparatus using the electrical actuator mechanism of the type described above, wiring from the brake pedal can be simplified, but the actuator body opposing the disc is large. The construction of the actuator mechanism is complicated, resulting in high cost and high power consumption. As a result, there is much room for improvement in this conventional brake apparatus.